Page 1

Anatomy and Stretching 101

Extensor muscles of forearm The muscles of the posterior compartment of the forearm are illustrated below and their attachments, innervation, and main actions of them are provided by layer in Table 1.

Table 1. Muscles of posterior compartment of forearm Muscle

Proximal Attachment

Distal Attachment


Main Action(s)

Superficial layer Brachioradialis

Proximal two thirds of supraepicondylar ridge of humerus

Lateral surface of distal end of radius proximal to styloid process

Radial nerve (C5, C6, C7)

Relatively weak flexion of forearm; maximal when forearm is in midpronated position

Extensor carpi radialis longus (ECRL)

Lateral supraepicondylar ridge of humerus

Dorsal aspect of base of 2nd metacarpal

Radial nerve (C8, C7)

Extend and abduct hand at the wrist joint; ECRL active during fist clenching

Extensor capri radialis brevis (ECRB)

Lateral epicondyle of humerus (common extensor origin)

Dorsal aspect of base of 3rd metacarpal

Deep branch of radial nerve (C7, C8)

Extensor digitorum

Extensor expansions of medial four digits

Extends medial four digits primarily at metacarpophalangeal joints, secondarily at interphalangeal joints

Extensor digiti minimi (EDM)

Extensor expansion of 5th digit

Extends 5th digit primarily at metacarpophalangeal joint, secondarily at interphalangeal joint

Dorsal aspect of base of 5th metacarpal

Extends and adducts hand at wrist joint (also active during fist clenching)

Extensor carpi ulnaris (ECU)

Lateral epicondyle of humerus; posterior border of ulna via a shared aponeurosis


Proximal Attachment

Distal Attachment


Main Action

Deep layer Supinator

Lateral epicondyle of humerus; radial collateral and anular ligaments; supinator fossa; crest of ulna

Lateral, posterior, and anterior surfaces of proximal third of radius

Deep branch of radial nerve (C7, C8)

Supinates forearm; rotates radius to turn palm anteriorly or superiorly (if elbow is flexed)

Extensor indicis

Posterior surface of distal third of ulna and interosseous membrane

Extensor expansions of 2nd digit

Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve

Extends 2nd digit (enabling its independent extension); helps extend hand at wrist

Posterior interosseous nerve (C7, C8), continuation of deep branch of radial nerve

Abducts thumb and extends it at carpometacarpal joint

Outcropping muscles of deep layer Abductor pollicis longus (APL)

Posterior surface of proximal halves of ulna, radius, and interosseous membrane

Base of 1st metacarpal

Extensor pollicis longus (EPL)

Posterior surface of middle third of ulna and interosseous membrane

Dorsal aspect of base of distal phalanx of thumb

Extends distal phalanx of thumb at interphalangeal joint; extends metacarpophalangeal and carpometacarpal joints

Extensor pollicis brevis (EPB)

Posterior surface of distal third of radius and interosseous membrane

Dorsal aspect of base of proximal phalanx of thumb

Extends proximal phalanx of thumb at metacarpophalangeal joint; extends carpometacarpal joint

The spinal cord segmental innervation is indicated (e.g., “C7, C8� means that the nerves supplying the extensor carpi radialis are derived from the seventh and eights cervical segments of the spinal cord). Numbers in boldface (C7) indicate the main segmental innervation. Damage to one or more of the listed spinal cord segments or to the motor nerve roots arising from them results in paralysis of the muscles concerned.


Anatomy The extensor muscles are in the posterior (extensor-supinator) compartment of the forearm, and all are innervated by branches of the radial nerve These muscles can be organized physiologically into three functional groups: 1. Muscles that extend and abduct or adduct the hand at the wrist joint (Image 1) • extensor carpi radialis longus • extensor carpi radialis brevis • extensor carpi ulnaris IMAGE 1

Image 1. A “functional” group of muscles from the posterior forearm, described above.


2. Muscles that extend the medial four fingers (Images 2 & 3) • extensor digitorum • extensor indicis • extensor digiti minimi

Image 2. Extensor digitorum


Image 3. Extensor indici & extensor digiti minimi


3. Muscles that extend or abduct the thumb (Image 4) • abductor pollicis longus • extensor pollicis brevis • extensor pollicis longus

Image 4. Muscles that extend or abduct the thumb


• The extensor tendons are held in place in the wrist region by the extensor retinaculum, which prevents bowstringing of the tendons when the hand is extended at the wrist joint. Image 5. • As the tendons pass over the dorsum of the wrist, they are provided with synovial tendon sheaths that reduce friction for the extensor tendons . Image 5.

Additional information The extensor muscles of the forearm can also be organized anatomically into superficial and deep layers • Four superficial extensors • extensor carpi radialis brevis, • extensor digitorum, • extensor digiti minimi • and extensor carpi ulnaris • are attached proximally by a common extensor tendon to the lateral epicondyle • the other two muscles in the superficial group brachioradialis and extensor carpi radialis longus attach to the lateral supra-epicondylar ridge of the humerus and adjacent lateral intermuscular septum

Brachioradialis • The brachioradialis, a fusiform muscle, lies superficially on the anterolateral surface of the forearm. Images 6 - 8. • As mentioned previously, the brachioradialis is exceptional among muscles of the posterior (extensor) compartment in that it has rotated to the anterior aspect of the humerus and thus flexes the forearm at the elbow. • It is especially active during quick movements or in the presence of resistance during flexion of the forearm (e.g., when a weight is lifted), acting as a shunt muscle resisting subluxation of the head of the radius • The brachioradialis and the supinator are the only muscles of the compartment that do not cross and therefore are incapable of acting at the wrist IMAGE 6

Image 6. Brachioradialis, right arm


Image 7. Brachioradialis, right arm, lateral perspective


Image 8. Brachioradialis, right arm, posterior perspective

Stretches Forearm Extensors HOW TO STRETCH: Photo A - Kneel on floor placing backs of hands onto floor - Lean weight into hands and backwards


HOW TO CONTRACT: Photo B - Press back of hands down into floor


HOW TO RESTRETCH: Photo B - Press more weight down onto wrists/hands and lean back further

Major muscles stretched Forearm extensors

Try the following stretches for the lower trapezius (ascending fibers) and latissimus Dorsi muscles in particular..

Lying Bicep HOW TO STRETCH: Photo A - Place forearm and front of shoulder onto floor (forearm pronated, shoulder neutral if possible) - Hand of straight arm to be higher than head - Roll opposite hip, shoulder and leg backwards - Press opposite hand into floor



D HOW TO CONTRACT: Photo B - Press arm down into floor


Major muscles stretched Anterior deltoid Biceps brachi Brachialis Forearm extensors

HOW TO RESTRETCH: Photo C and D - Roll opposite hip, leg and shoulder further back - Press opposite hand into floor - Make a fist and flex wrist for greater forearm stretch

Biceps Brachii • Standard: Any • Spring Tension: Heavy • Muscle Emphasis: Biceps brachii, brachialis, anterior deltoid


A. How to stretch Stand or sit as pictured. Lift and straighten arm. Pronate forearm (turn thumb down). Lean away from strap ensuring carriage does not move.

A. How to contract

Attempt to pull on strap and bend elbow.


B. How to restretch Lean further from strap. Rotate chest away from arm.


C. What to watch for • Internally rotating shoulder of stretching arm. • Dropping stretching arm. • Allowing carriage to move. Photo C shows how to maintain good form.

Conclusion The stretches that require no equipment can be found in my book “StretchFit: Safe Effective Stretches for Every Body,” on Amazon books. The final stretches on the Pilates reformer is from “Stretching on the Pilates Reformer: Essential Cues and Images” on Amazon books.

Profile for Innovations in Pilates

Anatomy & Stretching Posterior Forearm  

Anatomy & Stretching Posterior Forearm